Catalytic vapor phase process for producing dihydrocarbyl carbonates

ABSTRACT

A process for the preparation of dihydrocarbyl carbonates comprising contacting an alkanol such as methanol, carbon monoxide and oxygen with a heterogeneous catalyst which comprises a metal halide such as cupric chloride or a mixed metal halide such as cupric chloride/potassium chloride impregnated on an appropriate support such as activated carbon; and a process for reactivating metal halide catalysts supported on porous carrier materials comprising drying and then contacting the supported catalysts with a gaseous stream of hydrogen halide for a period of time which is sufficient to convert all of the metal present in whatever form to the corresponding metal halide.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation in part of Applicant's co-pendingapplication Ser. No. 871,725, filed June 6, 1986, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to the carbonylation of alkanols. Morespecifically, it pertains to a process for carbonylating alkanols in thevapor phase in the presence of a heterogeneous catalyst to producedihydrocarbyl carbonates.

This invention also relates to a method for reactivating theheterogeneous catalyst used in the above process for carbonylatingalkanols in the vapor phase to produce dihydrocarbyl carbonates.

The carbonates produced by this invention are well-known and are usefulas synthetic lubricants, solvents and chemical intermediates in thepreparation of polymeric derivatives such as clear plastics.

The traditional method for producing carbonates involves contactingphosgene with an appropriate alcohol. See Drake et al., J. Am. Chem.Soc., 52, 3720 (1960) and U.S. Pat. No. 2,379,250. This method resultsin the production of hydrogen chloride and thereby leads to theundesirable production of chlorine-containing byproducts. In particular,the use of secondary alcohols leads to a significant formation of alkylchlorides. Attempts to neutralize the hydrogen chloride have led toprocessing difficulties.

Other methods of producing carbonates generally involve the homogeneousliquid phase reaction of an alkanol, carbon monoxide and oxygen in thepresence of a catalyst. For example, U.S. Pat. No. 4,360,477 describes amethod for carbonylating alkanols with carbon monoxide and oxygen atelevated temperatures in the presence of copper salts. U.S. Pat. No.4,370,275 discloses a process for preparing carbonates by reacting analcohol, carbon monoxide and oxygen in the presence of a catalyst systemcontaining copper, chemically bonded oxygen, chemically bonded halogenand at least one nitrogen base. The oxidative carbonylation processclaimed in U.S. Pat. No. 4,426,331 involves the reaction of carbonmonoxide, oxygen and an alcohol in the presence of a copper compound anda sulfone. U.S. Pat. No. 4,218,391 indicates that high acidity incarbonylation reactions involving metal salts leads to significantformation of by-products.

The above processes utilizing a homogeneous process require elaborateseparation techniques to separate the organic base promoter in theazeotropic mixtures which can form between the dialkyl carbonate and theby-product water or unreacted alkanol. In addition, complex distillationsteps are necessary to recover the catalysts for recycle to theprocesses. Due to the highly corrosive nature of most solutionscontaining copper halides and alkanols, expensive materials ofconstruction are required for the reaction vessels and pipelines.

The above processes also do not provide for an efficient method ofregenerating the catalysts used therein. Most catalysts can beregenerated by being subjected to acidic conditions. However, highlyacidic conditions in the actual reaction mixture can lead to significantby-product formation. Therefore, over-acidification of the catalyst canlead to lower selectivities.

A process for the catalytic production of dihydrocarbyl carbonates isneeded that would eliminate the above problems regarding separation anddistillation and that would facilitate the regeneration of the catalystutilized. An efficient method for regenerating the catalyst is alsoneeded that would not interfere with the selectivity of the catalyst.

SUMMARY OF THE INVENTION

The present invention is such a process for the production ofdihydrocarbyl carbonates and avoids many of the problems heretoforeencountered. The process of the present invention comprises contacting,in the vapor phase, an alkanol, carbon monoxide and oxygen with aheterogeneous catalyst containing a metal halide or mixed metal halideimpregnated on an appropriate support under reaction conditionssufficient to form a dihydrocarbyl carbonate. This heterogeneous processeffectively eliminates the need for elaborate separation techniques andcomplex distillation steps which were heretofore necessary in order toseparate the catalyst from the reaction product. The supported catalystis easily regenerated and the process can be carried out underrelatively mild conditions while minimizing the production of unwantedby-products. Furthermore, no organic base promoter, such as pyridine, isneeded since the support serves this function.

Another aspect of the present invention involves a method forreactivating the supported heterogeneous catalyst used in theaforementioned carbonylation reaction. The regeneration method comprisesdrying and contacting the catalyst with a gaseous stream of hydrogenhalide for a period of time which is sufficient to convert all of themetal present in whatever form to the corresponding metal halide. Thisregeneration process unexpectedly allows the carbonylation catalyst tobe treated under strongly acidic conditions without adversely affectingthe performance and selectivity of the catalyst.

DETAILED DESCRIPTION OF THE INVENTION

The metal halide useful in the practice of the present invention can beany metal halide that will effectively catalyze the carbonylationreaction contemplated herein. The metal is preferably selected from themetals in Groups VIIIA or IB. Preferred metals include copper, nickel,iron and cobalt. The metal is most preferably copper. The halide can bechloride, bromide, iodide or fluoride and is most preferably chloride.Preferred metal halides include cupric chloride, nickel chloride andiron chloride with cupric chloride being most preferred.

Mixed metal halide herein refers to a combination of the metal halidedescribed above with a second metal halide. The metal of the secondmetal halide is selected from Groups IA or IIA. Typical metals that canbe used in the second metal halide of the present invention includepotassium, sodium, lithium, magnesium, cesium and calcium. The metal ispreferably selected from Group IA with potassium being the mostpreferred metal. The halide can be chloride, bromide, iodide or fluorideand is most preferably chloride. Preferred mixed metal halides includecupric chloride/potassium chloride and cupric chloride/magnesiumchloride with cupric chloride/potassium chloride being most preferred.

Any support which will withstand the carbonylation conditions describedherein can be used in the process of the present invention. However,activated carbon is superior to other supports that may be used. The useof activated carbon as a support results in a significantly higher rateof reaction than the use of other commonly known supports. Furthermore,the selectivity of the reaction toward the dihydrocarbyl carbonate basedon the amount of carbon monoxide fed to the reaction is higher whenactivated carbon is used as the support in comparison to other commonlyused supports. It is preferred to use an acid-washed lignite activatedcarbon having a particle size in the range from 0.85 to 1.70 mm in theprocess of the present invention.

The metal halide may be supported on the carrier material by anystandard impregnation technique such as that disclosed in ExperimentalMethods in Catalytic Research, Vol. II, edited by R. B. Anderson and P.T. Dawson, Academic Press, New York, 1978. In the case of a mixed metalhalide, the two metal halides may be mixed together and impregnated ontothe support simultaneously or the metal halides may be impregnatedseparately.

Alcohols useful in this invention include any alcohol which isvaporizable under the reaction conditions. Preferred alcohols correspondto the formula R¹ OH wherein R¹ is C₁₋₆ alkyl, C₃₋₆ cycloalkyl, orbenzyl. R¹ is preferably C₁₋₆ alkyl, more preferably methyl, ethyl orpropyl, and most preferably methyl.

Preferred alcohols include methanol, ethanol, propanol, butanol,pentanol, hexanol, cyclopropanol, cyclobutanol, cyclopentanol,cyclohexanol and benzyl alcohol. More preferred alcohols are methanol,ethanol, propanol, butanol, pentanol and hexanol. Even more preferredalcohols are methanol, ethanol or propanol, with methanol being mostpreferred.

This process prepares dihydrocarbyl carbonates, wherein the hydrocarbylmoiety corresponds to the hydrocarbon portion of the alcohol used in thepreparation. Preferred carbonates correspond to the formula ##STR1##wherein R¹ is C₁₋₆ alkyl, C₃₋₆ cycloalkyl, or benzyl. R¹ is preferablyC₁₋₆ alkyl, more preferably methyl, ethyl or propyl, and most preferablymethyl.

Examples of carbonates prepared by this invention include dimethylcarbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate,dipentyl carbonate, dihexyl carbonate, dicyclopropyl carbonate,dicyclobutyl carbonate, dicyclopentyl carbonate, dicyclohexyl carbonate,dibenzyl carbonate, methylethyl carbonate, ethylpropyl carbonate,methylpropyl carbonate and the like. Preferred carbonates prepared bythis process include dimethyl carbonate, diethyl carbonate, dipropylcarbonate, dibutyl carbonate, dipentyl carbonate and dihexyl carbonate.Even more preferred carbonates are dimethyl carbonate, diethyl carbonateand dipropyl carbonate. The most preferred carbonate prepared by thisinvention is dimethyl carbonate.

In general, the alcohol or mixture of alcohols is contacted with oxygenand carbon monoxide under carbonylation conditions so as to prepare acarbonate. In the embodiment wherein a mixture of alcohols is used, thecarbonates prepared are a mixture of symmetrical and unsymmetricalcarbonates. When a single alcohol is used, the product is a symmetricalcarbonate. The symmetrical dihydrocarbyl carbonates are the preferredcarbonates.

The process of this invention involves contacting carbon monoxide,oxygen and an alcohol in the vapor phase and passing them over thesupported metal halide described hereinbefore. The process of thisinvention can be illustrated by the equation ##STR2## wherein R¹ is asdefined hereinbefore. The ratio of carbon monoxide to the alcohol can beany mole ratio which results in the preparation of the dihydrocarbylcarbonates. Preferably, the ratio of carbon monoxide to the alcohol isbetween about 1:1 and about 1000:1 moles. More preferably, the ratio ofcarbon monoxide to alcohol is between about 1:1 and about 100:1 moles,and most preferably, the ratio of carbon monoxide to alcohol is betweenabout 1:1 and about 10:1 moles. The ratio of oxygen to alcohols is anyratio which results in the preparation of the dihydrocarbyl carbonates.Preferably, the ratio of oxygen to alcohol is between about 1:1 andabout 1:1000 moles. More preferably, the ratio of oxygen to alcohol isbetween about 1:1 and about 1:100 moles. Most preferably, the ratio ofoxygen to alcohol is between about 1:1 and about 1:10 moles. The ratioof oxygen to carbon monoxide is any ratio which results in thepreparation of the dihydrocarbyl carbonates. Preferably, the ratio ofoxygen to carbon monoxide is between about 1:1 and about 1:1000 moles.More preferably, the ratio of oxygen to carbon monoxide is between about1:1 and about 1:100 moles, and most preferably, the ratio of oxygen tocarbon monoxide is between about 1:1 and about 1:10 moles.

The oxygen can be added to the reaction mixture as pure molecular oxygenor diluted with an inert gas such as nitrogen or argon. It is preferredto keep the oxygen concentration at no more than 10 mole percent of theentire reaction feed so as to avoid the formation of explosive mixtures.

This process can be performed at any temperature and pressure at whichthe reaction proceeds. Preferred temperatures are between about 20° C.and about 150° C., with between about 90° C. and about 125° C. beingmore preferred. The most preferred temperatures are between about 115°C. and about 125° C. The pressure can be atmospheric or superatmosphericpressure. Preferred pressures are between about 1 and about 100atmospheres, with between about 15 and about 25 atmospheres being mostpreferred.

The reaction mixture feed gas flow rate, expressed as gas hourly spacevelocity, can be between about 100 and about 50,000 (Hr⁻¹), and mostpreferably, between about 1,000 and about 2,000 (Hr⁻¹). Thedihydrocarbyl carbonate can be recovered from the reaction mixture bymethods well-known in the art. One particularly desirable method is theuse of extractive distillation of the condensed reaction product.

The process of this invention can be performed in either a fixed orfluid bed reactor using either continuous or batch processing methods.It is preferred to use a fixed bed reactor and a continuous mode ofoperation.

One way of expressing the reaction rate at which product is produced isby the use of a turnover number. A turnover number is defined as thenumber of moles of product produced per gram atom of metal in thecatalyst per second. It is preferred that at least about 5.0×10⁻⁵ molesof product are produced per gram atom of metal in the catalyst persecond. It is more preferred that at least about 2.3×10⁻⁴ moles ofproduct are produced per gram atom of metal in the catalyst per second.It is even more preferred that at least about 4.5×10⁻⁴ moles of productare produced per gram atom of metal in the catalyst per second. In themost preferred embodiment, at least about 5.0×10⁻⁴ moles of product areproduced per gram atom of metal in the catalyst per second. In the caseof a mixed metal halide, the metal of the second metal halide is notconsidered in determining the turnover number or reaction rate. Asdiscussed above, the second metal halide is the metal halide wherein themetal is selected from Groups IA or IIA. Selectivities to thedihydrocarbyl carbonate based on the alcohol preferably range from atleast about 75 to 85 percent.

The other aspect of the present invention involves regeneration of thecatalyst hereinbefore described. After many hours of use, the activityof the catalyst as measured by the turnover number, i.e. the number ofmoles of carbonate produced per gram atom of copper in the catalyst persecond, decreases. The regeneration method provides a sequence ofcatalyst treatment steps comprising drying the catalyst and contactingthe catalyst with a gaseous stream of hydrogen halide, preferablydiluted with an inert gas, at a sufficient temperature and for asufficient period of time to convert essentially all of the metalpresent in whatever form to the metal halide. This regeneration processresults in the regenerated catalyst showing activity comparable to freshcatalyst.

Without wishing to be bound by any theory, it is believed that the metalhalide catalysts of this invention are deactivated due to loss of thehalide ligand which is replaced by hydroxide. The hydroxide is in turnreplaced by the halide by the regeneration process of this invention.

The regeneration process basically comprises two major steps. The firststep comprises heating the catalyst in the presence of an inert gas at asufficient temperature and for a sufficient amount of time so as toremove moisture. The second step involves subjecting the dried catalystto gaseous hydrogen halide which has preferably been diluted with aninert gas or air for a sufficient amount of time and at an appropriatetemperature to effectively reactivate the catalyst. If desired, theregenerated catalyst may be freed of adsorbed HCl by purging with aninert gas.

Typical inert gases useful in the present invention include nitrogen,helium and argon, with nitrogen and helium being preferred. The mostpreferred inert gas for the first step is nitrogen. Air is mostpreferred for the second step for reasons of convenience and economy.

The first or drying step can be carried out at any temperaturesufficient to effectively remove a substantial amount of moisture fromthe catalyst. The precise amount of moisture removed from the catalystis not critical but should be an amount sufficient to preventsubstantial interference with catalytic activity. Drying temperaturesuseful in the practice of this invention range from about 90° C. toabout 300° C., with about 115° C. to about 140° C. being preferred.Typical first step drying times range from about 0.1 to about 24 hours,with 2 to 4 hours being preferred. The first step can be carried out atany pressure sufficient for elimination of moisture. Typical pressuresrange from about 0.1 to about 500 psi with atmospheric pressure beingpreferred for convenience. The inert gas flow rate can range frombetween about 0.025 to about 250 cc (STP) per cc of catalyst per hour.Preferably, the inert gas flow rate ranges between 10 and 50 cc (STP)per cc of catalyst per hour, with about 30 cc (STP) per cc of catalystper hour being most preferred.

The hydrohalogenation step can be carried out at any temperaturesufficient to reactivate the catalyst. Typical temperatures range fromabout ambient temperature to about 300° C. and preferably range fromabout 110° C. to about 150° C. The catalyst is subjected tohydrohalogenation from between about 0.1 to about 24 hours with betweenabout 0.5 and 2 hours being preferred. Typical pressures involved in thehydrohalogenation step range between about 0.1 to about 500 psi withatmospheric again being preferred for convenience. The typical gas flowrates in the hydrohalogenation step range from between about 0.025 toabout 250 cc (STP) per cc of catalyst per hour with between about 20 andabout 60 cc (STP) per cc of catalyst per hour being preferred. When aninert gas or air is used to dilute the hydrogen halide, the hydrogenhalide is present in the inert gas or air in concentrations ranging fromabout 0.1 to about 99 mole percent based on the inert gas or air, withbetween about 5 and about 20 mole percent of hydrogen halide beingpreferred.

SPECIFIC EMBODIMENTS

The following examples are included for the purposes of illustrationonly and are not to be construed to limit the scope of the invention orclaims. Unless otherwise indicated, all parts and percentages are byweight.

EXAMPLE 1

On a commercial activated carbon (DARCO*, 20 g, 0.85-1.70 mm) issupported 2.5 g of CuCl₂ from an ethanol solution by standardimpregnation techniques. The dried catalyst is analyzed as 4.37 weightpercent copper. Into a 1/2-inch outside diameter flow reactor operatedat 115° C. and at 20 atm pressure is loaded 1.6 g of catalyst. A flowconsisting of 80 cc (STP) per minute of CO and 13 cc (STP) per minute ofoxygen is passed through the reactor. Liquid methanol is fed to avaporizer operated at 185° C. with an LC pump which allows small amountsof CH₃ OH to be added to the system under pressure. A flow of CH₃ OHvapor of 30 cc (STP) per minute is introduced into the CO/O₂ feed streamprior to flowing through the reactor. The reaction products arecontinuously monitored on-line by standard gas chromatographytechniques. Dimethyl carbonate is produced at a rate of 5.3 to 5.5×10⁻⁴moles per gram atom of copper per second with 80 percent selectivitybased on methanol.

EXAMPLE 2

A CuCl₂.KCl catalyst (20 weight percent CuCl₂ and 5 weight percent KCl)is supported on lignite activated carbon by standard impregnationtechniques. A feed composed of 60 mole percent CO, 25 mole percent CH₃OH and 15 mole percent O₂ at a gas hourly space velocity of 1800 hr⁻¹ isfed to a 1/2 inch outside diameter flow reactor operated at 110° C. and20 atmospheres pressure. The reaction products are continuouslymonitored on-line by standard gas chromatography techniques. Dimethylcarbonate is produced at a rate of 6.0×10⁻⁴ moles of dimethyl carbonateper gram atom of copper per second.

COMPARATIVE EXAMPLE 1 (Not an embodiment of this invention)

Example 2 is repeated with the only difference being that a differentcatalyst is used in place of the CuCl₂.KCl on activated carbon. Thecatalyst is prepared by dissolving poly-4-vinylpyridine in methanol andadding this solution to CuCl in CH₃ CN according to the processdescribed in U.S. Pat. No. 3,980,690. Dimethyl carbonate is produced ata rate of 0.6×10⁻⁴ moles of dimethyl carbonate per gram atom of copperper second. This comparative example demonstrates the superiority ofCuCl₂.KCl supported on activated carbon as a catalyst in the productionof dimethyl carbonate.

EXAMPLE 3

The procedure used in Example 1 is repeated with the only differencesbeing that mixed metal halide catalysts are used in place of the CuCl₂catalyst in successive runs and that the activity of the differentcatalyst systems is measured as a function of time. These results areshown in Table I below.

                  TABLE I                                                         ______________________________________                                                  Turnover Number × 10.sup.4                                              (moles of DMC per g atom of Cu per sec)                                       Time (hours)                                                        Catalyst*   20    30       40  50     60  90                                  ______________________________________                                        CuCl.sub.2  5.3   4.7      4.4 3.8    3.6 --                                  CuCl.sub.2 /KCl                                                                           5.2   5.3      5.3 5.2    5.1 3.8                                 CuCl.sub.2 /MgCl.sub.2                                                                    4.5   4.4      4.5 4.6    4.4 3.6                                 ______________________________________                                         *20 Weight percent CuCl.sub.2 based on the total weight of catalyst           5 Weight percent additive (KCl or MgCl.sub.2) based on total weight of        catalyst                                                                 

The data shown above demonstrate that while CuCl₂ used alone has aninitially slightly higher activity, the addition of 5 weight percent ofKCl or MgCl₂ as an additive retards the rate of the deactivation of thecatalyst system.

EXAMPLE 4

The reactor in Example 1 is purged with nitrogen and cooled to roomtemperature. The catalyst of Example 1 is heated to 125° C. in nitrogen(125 cc STP per minute) and held at that temperature for 2 hours toremove moisture. The catalyst is chlorinated by passing a mixture of 10percent HCl/90 percent N₂ (175 cc STP per minute) through the reactorfor 3 hours and then cooling the catalyst to room temperature whilemaintaining the HCl/N₂ flow. The reactivated catalyst exhibits anactivity of 5.1×10⁻⁴ moles of dimethyl carbonate per gram atom of copperper second, indicating that the activity of the aged catalyst is almostcompletely returned to that of the fresh catalyst.

EXAMPLE 5

A CuCl₂ catalyst is subjected to neutron activation and x-raydiffraction measurements when it is fresh, when it has been used about90 hours in a procedure as given in Example 1, and when it has beentreated in a regeneration process where the catalyst is treated for onehour in flowing 10%HCl/90%N₂ followed by a three hour N₂ purge. Theseresults are given in Table II below.

                  TABLE II                                                        ______________________________________                                        Chemical Analysis by Neutron Activation                                       and X-ray Diffraction Measurements                                            on Selected Darco-Supported CuCl.sub.2 Catalysts                                                                Ratio                                                    Copper     Copper    Chloride/                                                Crystalline                                                                              Loading   Copper                                      Catalyst Sample                                                                            Phases     (wt %)    (wt %)                                      ______________________________________                                        Fresh        --         5.1 ± 0.2                                                                            1.10(1.12).sup. ○1                   (10.3 wt % CuCl.sub.2)                                                        Used         Cu(OH)Cl   5.1 ± 0.2                                                                            0.24                                        (90 hours)   Cu.sub.2 (OH).sub.3 Cl                                           HCl          Cu2(OH).sub.3 Cl                                                                         5.2 ± 0.3                                                                            1.12                                        Treated.sup. ○2                                                                     (trace)                                                          ______________________________________                                         .sup. ○1  Theory                                                       .sup. ○2  Treatment: One hour in flowing 10% HCl/N.sub.2 at            125° C. followed by threehour N.sub.2 purge                       

The information in Table II shows that the regeneration process resultsin a regenerated catalyst not significantly different in coppercrystalline phases, weight ratio of chloride to copper or in copperloading from a fresh catalyst.

EXAMPLE 6

The procedure followed in Example 1 is repeated using a CuCl₂ catalystsupported on activated carbon which undergoes a regeneration process asdescribed in Example 4. The activity of the catalyst as indicated by theturnover number is shown in Table III. The data is collected over a400-hour period.

                  TABLE III                                                       ______________________________________                                                 starting   Ending     Elapsed                                                                              %                                       Catalyst T.N.* × 10.sup.4                                                                   T.N.* × 10.sup.4                                                                   time (hr)                                                                            decrease                                ______________________________________                                        fresh    4.9        3.1        50     40                                      regenerated                                                                            4.6        3.2        40     30                                      one time                                                                      regenerated                                                                            4.5        3.2        50     27                                      two times                                                                     regenerated                                                                            4.8        3.2        90     32                                      three times                                                                   regenerated                                                                            4.3        2.6        100    39                                      four times                                                                    ______________________________________                                         *T.N. = turnover number (moles of DMC per g atom of Cu per sec)          

The data in the above table shows that the regenerated catalyst showscomparable activity with a fresh catalyst and further suggests that theregenerated catalyst is actually more stable than a fresh catalyst as ittakes longer for the catalyst activity to decrease.

The above examples show that a catalyst comprising a metal halide or amixed metal halide supported on activated carbon is effective incatalyzing the formation of dihydrocarbyl carbonate. Further, theexamples demonstrate that it is possible to simply and effectivelyregenerate such a catalyst.

What is claimed is:
 1. A process comprising contacting oxygen, carbonmonoxide and an alkanol, which can be vaporized under the reactionconditions, in the vapor phase, in the presence of a heterogeneouscatalyst which consists essentially of a metal halide or a mixed metalhalide impregnated on activated carbon under reaction conditionssufficient to produce a dihydrocarbyl carbonate.
 2. The process of claim1 wherein the dihydrocarbyl carbonate is produced at a rate expressed bya turnover number of at least about 4.5×10⁻⁴ moles of dihydrocarbyl pergram atom of metal per second.
 3. The process of claim 2 wherein thedihydrocarbyl carbonate is produced at a rate expressed by a turnovernumber of at least about 5.0×10⁻⁴ moles of dihydrocarbyl per gram atomof metal per second.
 4. The process of claim 1 wherein the alkanol is aC₁₋₆ alkanol, a C₃₋₆ cycloalkanol or benzyl alcohol, or mixturesthereof, and the hydrocarbyl groups on the dihydrocarbyl carbonate areseparately in each occurrence C₁₋₆ alkyl, C₃₋₆ cycloalkyl or benzyl. 5.The process of claim 3 wherein one alkanol is used and the dihydrocarbylcarbonate prepared is symmetrical.
 6. The process of claim 5 wherein thealkanol is a C₁₋₆ alkanol and the dihydrocarbyl carbonate is a C₁₋₆dialkyl carbonate.
 7. The process of claim 6 wherein the alkanol ismethanol and the dihydrocarbyl carbonate is dimethyl carbonate.
 8. Theprocess of claim 7 wherein the metal halide is a cupric halide.
 9. Theprocess of claim 8 wherein the cupric halide is cupric chloride.
 10. Theprocess of claim 9 wherein the mixed metal halide consists of cupricchloride and potassium chloride.
 11. The process of claim 10 wherein theactivated carbon is an acid-washed lignite carbon.
 12. A process for thepreparation of dimethyl carbonate comprising(1) supporting cupricchloride on activiated carbon, (2) loading the supported cupric chlorideinto a flow reactor operated at 115° C. and 20 atm, (3) passing a streamof 80 cc (STP) per minute of carbone monoxide and 13 cc (STP) per minuteof oxygen through the reactor, and (4) introducing 30 cc (STP) perminute of methanol vapor into the carbon monoxide/oxygen stream prior toflowing through the reactor wherein the selectivity to dimethylcarbonate is at least about 80 percent based on the methanol and theturnover number is at least 5.0×10⁻⁴ moles of dimethyl carbonate pergram atom of copper per second.
 13. A process for the preparation ofdimethyl carbonate comprising(1) supporting cupric chloride/potassiumchloride on activiated carbon, (2) loading the supported cupricchloride/potassium chloride into a flow reactor operated at 115° C. and20 atm, (3) passing a stream of 80 cc (STP) per minute of carbonmonoxide and 13 cc (STP) per minute of oxygen through the reactor, and(4) introducing 30 cc (STP) per minute of methanol vapor into the carbonmonoxide/oxygen stream prior to flowing through the reactor wherein theselectivity to dimethyl carbonate is at least about 80 percent based onthe methanol and the turnover number is at least about 5.0×10⁻⁴ moles ofdimethyl carbonate per gram atom of copper per second.